A polyphenylene ether resin, as is widely known, excels in heat resistance, mechanical properties, electrical properties, and so on and, therefore, is finding extensive utility as useful engineering plastics. Thus, the high heat resistance constitutes per se one of the salient features of a polyphenylene ether resin. This resin, nevertheless, has poor moldability because of a high melt viscosity and, further, tends to deteriorate at elevated temperatures possibly to the extent of even impairing its intrinsic properties. The adverse effects of these undesirable properties are conspicuous particularly on impact resistance.
To improve the impact resistance and the moldability of a polyphenylene ether resin, U.S. Pat. No. 3,383,435, for example, proposes incorporation of polystyrene in the polyphenylene ether resin and demonstrates that the impact resistance as well as the moldability is improved by the use of a rubber-modified polystyrene. Although the moldability is indeed improved in this resin composition, the impact resistance is not completely satisfactory from a practical point of view and the mold release property is not necessarily desirable. For improvement of impact resistance, several methods resorting to incorporation of a varying rubbery elastomer in the aforementioned composition (as in U.S. Pat. No. 3,660,581, U.S. Pat. No. 3,994,856, Japanese Patent Publication No. SHO 47(1972)-32781, Japanese Patent Publication No. SHO 57(1982)-56941, and Japanese Patent Application Laid-open No. SHO 53(1978)-72248) have been proposed. When the rubbery elastomer is added in a small amount, the effect of the addition is meager. When it is added in a large amount, the added elastomer impairs the melt flowing property of the composition and causes the appearance and mold release properties of the molded product of the composition to be degraded.